build(deps-dev): bump mypy from 1.18.2 to 1.19.0

[dependabot]

Bumps mypy from 1.18.2 to 1.19.0.

Changelog

Sourced from mypy's changelog.

Mypy Release Notes

Next Release

Drop Support for Python 3.9

Mypy no longer supports running with Python 3.9, which has reached end-of-life. When running mypy with Python 3.10+, it is still possible to type check code that needs to support Python 3.9 with the --python-version 3.9 argument. Support for this will be dropped in the first half of 2026!

Contributed by Marc Mueller (PR 20156).

Mypy 1.19

We’ve just uploaded mypy 1.19.0 to the Python Package Index (PyPI). Mypy is a static type checker for Python. This release includes new features, performance improvements and bug fixes. You can install it as follows:

python3 -m pip install -U mypy

You can read the full documentation for this release on Read the Docs.

Python 3.9 Support Ending Soon

This is the last mypy feature release that supports Python 3.9, which reached end of life in October 2025.

Performance Improvements

• Switch to a more dynamic SCC processing logic (Ivan Levkivskyi, PR 20053)
• Speed up type aliases (Ivan Levkivskyi, PR 19810)

Fixed‑Format Cache Improvements

Mypy uses a cache by default to speed up incremental runs by reusing partial results from earlier runs. Mypy 1.18 added a new binary fixed-format cache representation as an experimental feature. The feature is no longer experimental, and we are planning to enable it by default in a future mypy release (possibly 1.20), since it's faster and uses less space than the original, JSON-based cache format. Use --fixed-format-cache to enable the fixed-format cache.

Mypy now has an extra dependency on the librt PyPI package, as it's needed for cache serialization and deserialization.

Mypy ships with a tool to convert fixed-format cache files to the old JSON format. Example of how to use this:

$ python -m mypy.exportjson .mypy_cache/.../my_module.data.ff

... (truncated)

Commits

• 0f068c9 Remove +dev
• 6d5cf52 Various updates to 1.19 changelog (#20304)
• 3c81308 Add draft version of 1.19 release notes (#20296)
• 1999a20 [mypyc] librt base64: use existing SIMD CPU dispatch by customizing build fla...
• 1b94fbb [mypyc] Fix vtable pointer with inherited dunder new (#20302)
• 13369cb [mypyc] Fix crash on super in generator (#20291)
• a087a58 Update import map when new modules added (#20271)
• 35e843c [mypyc] Add efficient librt.base64.b64decode (#20263)
• 094f66d [mypyc] Add repr to AssignmentTarget subclasses (#20258)
• 0738db3 Do not push partial types to the binder (#20202)
• Additional commits viewable in compare view

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Summary by CodeRabbit

• Chores

  • Updated mypy development dependency to version 1.19.0 with enhanced platform-specific compatibility markers.

• Documentation

  • Added clarification regarding mypy installation compatibility with alternative Python implementations.

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[fizyk]

@CodeRabbit review changes

[coderabbitai]

@fizyk: I'll review the changes in this PR for you.

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Walkthrough

The mypy development dependency is upgraded from version 1.18.2 to 1.19.0 with environment markers restricting installation to CPython implementations only. A documentation fragment is added to record this constraint for future reference.

Changes

Cohort / File(s)	Summary
Dependency & Documentation Updates Pipfile, newsfragments/1127.misc.rst	Mypy dev-package version bumped to 1.19.0 with added CPython-only environment markers. Documentation fragment added to document the pypy exclusion policy.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

• Straightforward dependency version bump with environment marker addition
• Simple documentation fragment with no code logic
• No complex interactions or branching logic to validate

Poem

A rabbit hops past PyPy's door,
Says mypy now: "I'll skip this shore!"
CPython's friend, version new—
Markers guide the way through. 🐰✨

✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch dependabot/pip/mypy-1.19.0

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📥 Commits

Reviewing files that changed from the base of the PR and between b549907 and d7f089d.

📒 Files selected for processing (2)

• Pipfile (1 hunks)
• newsfragments/1127.misc.rst (1 hunks)

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@fizyk: I'll review the mypy dependency update from 1.18.2 to 1.19.0 for you.

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